1. Field of the Invention
The present invention relates to a zoom lens, and more particularly, to a zoom lens suitable for a photographic lens used in an image pickup apparatus such as a digital camera, a video camera, a monitoring camera, a broadcasting camera, and a silver-halide film camera.
2. Description of the Related Art
As an image pickup apparatus is miniaturized with a high functionality, a photographic lens used in the image pickup apparatus is required to be a zoom lens which has a short lens length in entirety, a small size, a wide angle of view, and a high zoom ratio.
As a positive lead type zoom lens, there is known a four-unit zoom lens including a first lens unit of a positive refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, and a fourth lens unit of a positive refractive power in order from an object side to an image side, in which all of the lens units are moved during zooming. As the four-unit zoom lens, there is known a miniaturized zoom lens in which the first lens unit includes negative and positive lenses, and a zoom ratio of 4 to 10 can be obtained. In addition, as the positive lead type zoom lens, there is known a five-unit zoom lens including a first lens unit of a positive refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, a fourth lens unit of a negative refractive power, and a fifth lens unit of a positive refractive power in order from an object side to an image side.
In the related art, in order to reduce a thickness of the camera, a retractable system is used, in which a distance between lens units when it is not used is reduced in comparison with a distance between lens units when it is used. In the retractable system, in order to effectively reduce a thickness of the camera, it is useful to increase the refractive power of each lens unit and reduce the number of lenses of each lens unit and the thicknesses of the lens units.
However, if the refractive power of each lens surface increases, the lens thickness increases to obtain a lens edge thickness. In particular, a front lens diameter increases, so that it is difficult to achieve miniaturization. In addition, various types of aberration such as chromatic aberration are frequently generated at a telephoto end, and it is difficult to correct such aberration.
In the four-unit or five-unit zoom lens described above, in order to miniaturize the entire zoom lens and implement excellent optical performance with a high zoom ratio, it is important to appropriately set configurations of each lens unit, movement conditions for zooming, and the like. In particular, it is important to appropriately set the movement amounts of the first, second, and third lens units for zooming.
U.S. Pat. No. 7,830,613 discusses a lens configuration capable of advantageously obtaining a thin thickness at the time of retraction of the zoom lens by reducing the number of lenses. However, since the movement amount of the first lens unit for zooming is large in comparison with the movement amount of the third lens unit, the entire lens length at the telephoto end tends to increase. In addition, since the movement amount of the first lens unit is large, the number of retraction stages increases, and a lens barrel configuration becomes complicated. In addition, the size of the zoom lens increases in a radial direction thereof.
U.S. Pat. No. 7,430,079 discusses a zoom lens having a zoom ratio of about 10 times, in which the entire lens length is reduced at a telephoto end by restricting a movement amount of the first lens unit during zooming. However, it is difficult to reduce a thickness of the camera at the time of retraction due to a ratio between the movement amount of the second lens unit for zooming and a focal length at a wide-angle end. In addition, as the refractive power of the first lens unit increases, axial chromatic aberration, chromatic aberration of magnification, and the like are frequently generated at a telephoto end, and it is difficult to correct such aberration.